The present invention relates separating sheets one by one from a pile of stacked sheets and feeding the thus separated sheets and more particularly, to a method and an apparatus suitable for use with equipment such as copying machines or printers in which a rapid and sure separation and feeding of the sheets is required.
In such equipment as a copying machine or a printer which contains a pile of sheets, it is required to pick or take out the sheets one by one from the pile of sheets and to convey the removed sheets to a predetermined position such as a printing section. A typical sheet feeding apparatus for this purpose has been disclosed in Japanese Patent Unexamined Publication No. 62-11184, and corresponding U.S. Pat. No. 4,678,176 where a vacuum-feeding device is arranged above the pile of sheets and a compressed air plenum chamber is provided adjacent to the pile of sheets.
In the sheet feeding apparatus disclosed in Japanese Patent Unexamined Publication No. 62-11184, the uppermost sheet of the piled sheets is floated up by air jet discharged from the compressed air plenum chamber, drawn or attracted and conveyed by the vacuum-feeding device. The vacuum-feeding device includes a vacuum chamber and an endless belt running around this vacuum chamber, and the endless belt is formed with a plurality of apertures for drawing the sheet through a negative pressure in the vacuum chamber. This publication also discloses an improved air knife which is provided for separating an upper portion of the sheet pile as a whole and includes horizontal air nozzles and other air nozzles for converging the air flow from the horizontal nozzles.
A sheet feeding apparatus of this type has also been disclosed in Japanese Patent Unexamined Publication Nos. 62-111844 and 62-111845, in each of which the conveying belt is divided into several sections with ribs interposed between these sections, and, a hopper on which the sheets are stacked is provided with claws for preventing more than two sheets from being taken out at once.
Further, Japanese Patent Unexamined Publication No. 62-93130 teaches taking-out of a sheet from the lowest portion of a sheet pile by using a vacuum-feeding apparatus which is similar to those disclosed in the above-mentioned publications.
Similarly, Japanese Patent Unexamined Publication No. 62-93141 discloses a feeding device which includes a vacuum chamber and a conveying belt cooperative with the vacuum chamber, and in which a sheet is drawn by the belt through a negative pressure in the vacuum chamber and conveyed by the belt. In this publication,it has been taught that the conveying belt is driven intermittently and formed with a plurality of through holes which are arranged over the length corresponding to one stroke of the intermittent drive motion.
It is desirous that various sheets can be surely separated and fed regardless of their types and thicknesses, because the sheets used in copying machines or printers have been diversified. It is also desired to decrease the time period required for the sheet separation and feeding for achieving more rapid operation of such an equipment as copying machine or printer.
Relating to the conveyance of sheets following to the taking-out thereof described in this application, the present inventors et al have filed U.S. application Ser. No. 395,015 titled as "METHOD AND APPARATUS FOR ADJUSTING POSTURE OF SHEET" on Aug. 17, 1989.